Cleaners at the Marine Corps museum near Quantico noticed spots on windows they thought were bird droppings one recent Sunday. They turned out to be bullet holes.

Since that discovery, the same weapon has been used four more times to fire at U.S. military facilities in Northern Virginia.

The gunman has taken aim only at night or early in the morning, when the buildings would be vacant or sparsely populated, and authorities said they don’t think he or she is out to hurt anyone. The shooter might be trying to send a message, officials said, but they don’t know what the message is. As they search for the person, the questions remain: Who and why?

“Sometimes it is just for the thrill,” said James Alan Fox, a criminologist at Northeastern University in Boston. “Sometimes it’s for the sake of power and control. Or maybe he just wants to wreak havoc on the military.”

The incidents began the night of Oct. 16. or early the next morning, when shots were fired at the National Museum of the Marine Corps in Triangle. The Pentagon was hit a few days later. A U.S. Marine recruiting center in Chantilly was next. Then the shooter returned to the Marine Corps museum.

On Wednesday, authorities announced that a fifth shooting of a U.S. military facility in Northern Virginia was part of the same spree. This time shots were fired at a U.S. Coast Guard recruiting center in Woodbridge. As in the other cases, no one was injured.

How many of these types of facilities are in the area? You’d think law enforcement would have them all pretty much staked out by now. Whoever the sniper is, they’re fairly consistent as to the type of target and when they operate. It would be a good thing if the sniper was caught before they change their mind and start shooting people instead of buildings.

/anyway, the sniper still needs the Air Force, Army, and Navy to collect the complete set of service branches